Are We Nearer to NEXCOM?

Full-scale development of FAA’s next-generation air/ground communications system has yet to begin. Nevertheless, the program progresses, and Phase 1 apparently is on track.

James W. Ramsey

The Federal Aviation Administration’s (FAA’s) next-generation air/ground communications system (NEXCOM) program is showing steady progress, and its first phase appears to be on schedule, despite industry controversy over the agency’s priorities.

Some aviation industry officials disagree with FAA’s decisions on not expanding the U.S. controller pilot data link communications (CPDLC) program and on the limited use of VHF digital link Mode 2. But FAA officials such as Dan Salvano, director CNS (communications, navigation and surveillance) systems, defend the decision to switch emphasis to NEXCOM, which they say may be the radio system of the 21st century. NEXCOM, including four-channel, digital/analog VHF digital link Mode 3 (VDL-3) as its pipeline for both voice and data communications, is advanced as the best solution for modernizing a 50-year old air/ground communications system. It is expected to:

Relieve predicted voice frequency saturation,

Accommodate the addition of air traffic control (ATC) sectors and services,

Provide a data link capability for CPDLC and other applications,

Replace expensive-to-maintain UHF and VHF analog radios, and

Allow for security mechanisms.

NEXCOM is not yet operational, but FAA officials believe they have sufficient time for its development. With the drop-off in air traffic following the Sept. 11 tragedy, congestion has been relieved, giving FAA time to evaluate NEXCOM or its alternatives.

"In Europe they have a spectrum problem that is forcing them to make a decision," says Salvano. "In the U.S. we don’t have to make an immediate decision–whether it be 8.33-kHz spacing, VDL-2 or VDL-3–based on spectrum depletion. We have time to make that deployment decision."

Program Progresses

FAA awarded a contract for a ground-based multimode digital radio–the first of four elements in the NEXCOM program– to ITT Industries in 2001. The agency plans to gradually replace its network of some 46,000 VHF and UHF ground stations that have remained virtually unchanged since the 1940s. The new radios are a near-term improvement and are upgradable to the new VDL Mode 3 system. A separate contract was awarded in 2002 to General Dynamics to replace the UHF radio infrastructure used to talk to the military.

"All the radios don’t need to be replaced immediately," says Jim Williams, FAA’s Communications IPT (integrated product team) leader. "We’ll try to replace the oldest ones in the en route structure, and then follow-on contracts may be required to replace the terminal infrastructure. So it’s a long-term process." The goal is to have the new radios in place to prepare for whatever option the NEXCOM program will take.

The multimode radios "have the capability to do 25-kHz or 8.33-kHz channelization–both of these are analog–or the digital VDL Mode 3," says Williams. "If you plug them into a digital channel, they will become digital. They are multimode, the same as the airborne radios."

FAA is not ready to say that the multimode radios are intended for VDL-3. "We have not made that decision," says Salvano. "The multimode radios will be fitted into the system as it exists today–initially in the 25-kHz analog mode. But if we decide on another capability, they can accommodate that." (A capability FAA doesn’t plan for the new radios is VDL Mode 2.)

Rapid Prototyping on Target

The NEXCOM program’s ground system rapid prototype development effort (RPDE) is on target after contracts were awarded in February 2003 to Harris ($21 million) and ITT ($16 million) for a 20-month initial phase competition that will run through the end of 2004. The two companies will compete for the program’s next, or full-scale development (FSD), phase–scheduled to be awarded in July 2005, after an FAA Joint Resource Council (JRC) decision on the program’s future.

FAA will gain more than NEXCOM system options from the competition. "It helps us understand the technical issues, what’s achievable, and gives us a good idea of what [the system] will cost and how long it’s going to take," says Williams. That information will be presented to the JRC, which will make the go or no-go decision. "If the JRC says yes, we make the down-select between the two vendors based on who has the best results," Williams adds.

FAA requires Harris and ITT to produce a technical document package (TPD) that includes architecture, equipment specifications and supporting technical documents for NEXCOM. They also are to develop engineering design models (EDMs) of NEXCOM ground network systems, including hardware and software, and use them to demonstrate a set of "high-risk" capabilities, explains Ron Demuynck, NEXCOM program manager for Harris. Both contractors are to make an EMD demonstration near the end of the RPDE program, in October 2004, at the FAA’s Technical Center in Atlantic City, N.J.

This is a "private test" and will be used to evaluate our performance on the contract," says Demuynck. "And that will be factored into the award decision for the FSD phase."

With experience as a communications systems integrator for FAA and involvement in the NEXCOM program since the early 1980s, Harris leads a team that includes Raytheon, Computer Sciences Corp. (CSC), Lockheed Martin ATM, Rockwell Collins and Avidyne.

Collins and Avidyne are the avionics teammates. Raytheon is developing the hardware and software design of the infrastructure, while Lockheed Martin, contractor for FAA’s En Route Automation Modernization (ERAM) program, is helping Harris with the interface to that system. And General Dynamics is assisting with legacy interfaces, so the new system can accommodate analog UHF radios.

ITT also is on schedule in the competitive ground network development effort, according to Richard Eckert, ATC marketing manager. ITT leads a team that includes two of its own units–Aerospace and Communications and Advanced Engineering Services–and two Northrop Grumman units, Information Technology and Denro Systems, the latter of which provides voice switches. JDA Associates and Fourtier Group, which provide systems engineering services, round out the ITT team.

Avionics in Front

The NEXCOM program’s airborne element is well under way and apparently ahead of the ground portion. In December 2001, FAA signed cost-sharing agreements with Honeywell, Rockwell Collins and Avidyne to develop new airborne radio equipment capable of handling VDL Mode 3.

The original agreements called for Rockwell Collins and Honeywell to develop NEXCOM avionics for air transport aircraft and for Avidyne to target avionics for general aviation aircraft. A contract extension, awarded to Rockwell Collins in July 2003, added business jet customers as a target market.

The three avionics manufacturers stand to gain handsomely from the NEXCOM program. Industry sources estimate that if FAA were to mandate NEXCOM by the end of the decade, the air transport market alone would need 12,000 replacement radios worth $300 million for the 6,000-aircraft fleet.

Following a year-long development program, pre-production avionics systems were tested for interoperability. The tests were conducted in July 2003, using a Mitre-supplied, prototype ground system simulator at the FAA Tech Center. The three manufacturers’ products were tested simultaneously, "and all interoperated successfully," Williams reports.

The airborne systems were mounted on a pallet and tested on FAA’s B727 aircraft. The radios "talked" to the ground station simulator, according to Nancy Guzak, VHF program manager for Rockwell Collins. Subsequent to the air-to-ground tests, the center performed air-to-air testing to show that the three systems can communicate with each other.

Collins’ and Honeywell’s equipment packaging was the same, using the ARINC 750-compliant form/fit/function, with the radio located in the avionics bay and the tuning panel in the cockpit. Avidyne’s package for general aviation is contained in a single unit, mounted in the cockpit.

Collins was the first avionics supplier to successfully demonstrate CPDLC through the NEXCOM VDL Mode 3 ground network, Guzak maintains. Simultaneous digital voice and data, along with enhanced voice features of Mode 3, were demonstrated during the tests, which used Collins’ VHF-920A data radio and CMU-900 communications management unit, along with a Gables Engineering G7424-302 radio tuning panel.

In last July’s air-to-ground and air-to-air interoperability tests, Honeywell demonstrated its RTA-50D VDR (VHF data radio). The -50D was "developed for Nexcom, but also to serve as the company’s next-generation VDR radio," says Kevin Wohlers, Honeywell’s VHF program manager. The new radio includes all the functions of Honeywell’s RTA-44D radio, some 5,000 of which are in service. The -50D also could be used for Mode 2–and will add Mode 3. Also used by Honeywell in the tests was a CMU emulator, a PC simulating a CMU, to test Mode 3 data. Honeywell also used a radio tuning panel provided by Gables Engineering.

Honeywell plans to certify its Mode 3 avionics by mid-2004. It is talking to several airlines to arrange a partnership for certification and for the operational tests to follow. It expects to have certified Mode 3 radio equipment available for Boeing and Airbus aircraft by the end of 2004.

Wohlers feels that some airlines, which want the capabilities offered by the current -44D radio and "want to be Mode 3-ready," will opt to purchase the new -50D once the FAA ground infrastructure is in place. And while concentrating initially on the air transport market, Honeywell is looking at the business and regional aircraft markets as well, Wohlers says.

Avidyne says its radio for general aviation aircraft "will perform in the current environment, and also be capable of VDL," says spokesman Tom Harper. Avidyne is not ready to market the system yet, but plans to complete all the development work required for VDL Mode 3. He says Avidyne plans by 2005 or 2006 to have the digital radios as "part of an integrated flight deck" for higher-end GA aircraft, including jets.

The second interoperability demonstration of radios was scheduled for early November 2003 at Atlantic City. And in November 2004, a final exercise will employ the certified avionics, along with the new ITT multimode digital ground radios, "in a full-up operational suitability test," says Salvano.

Collins plans to certify its air transport avionics equipment on a Delta Air Lines B737NG beginning in April, with a target date of next July. The system will have to be certified on each aircraft type if VDL-3 is mandated, and airlines will have to accomplish certification for retrofit applications, says Guzak.

Avionics Upgrade

Both hardware and software changes are required to update current radios (including VDL-2-capable radios) to achieve Mode 3 capability. Accommodating digital voice involves adding a "vocoder" (voice coder/decoder). Airlines will be able to upgrade their Collins radios to Mode 3 via a company service bulletin either in a certified avionics shop or by sending them to a Rockwell Collins service center. Any of Collins’ Series 900 radios can be upgraded to Mode 3, thus securing all VHF data link modes, except Mode 4, a data link developed in Sweden and proposed for automatic dependent surveillance-broadcast (ADS-B), among other applications.

If you have a voice-only VHF radio, "you can upgrade and get both Mode 3 and Mode 2 [for data] at the same time," Guzak says. Similarly, with the CMU, "a bulletin upgrade will allow you to get from ACARS [aircraft communications addressing and reporting system], the standard data mode, to Mode 2 and then a further upgrade to get to Mode 3," she adds. "Or you could bypass Mode 2 and just go right to Mode 3, and get both [voice and data].

"So, depending on where you’re flying, if you need 8.33 kHz [currently required in Europe] or you need 25-kHz voice or you’re in an area with Mode 2 or Mode 3, the radio can switch automatically. Some of [the switching] is generated from the control panel, some of it–in the case of Mode 3–from the ground."

Collins has begun cost analysis research with Mitre. However, says Guzak, "depending on where you start from, if you acquire upgrade kits, the cost is nominal–definitely less than if you have to buy a new radio." But for those operators who don’t have upgradable radios, installing one "is the biggest hit," she adds.

NEXCOM Advantages

NEXCOM was conceived to prevent frequency saturation and accommodate additional ATC sectors and runways, as well as to replace the expensive-to-maintain VHF and UHF radios. FAA officials believe it also will relieve controller and pilot workload, providing features not currently available, such as the elimination of stuck microphones and channel blocking, reduced RF (radio frequency) interference, and improved system security.

For the latter benefit, an "urgent downlink" feature was instituted as a result of the Sept. 11 terrorist attack. "When a pilot needs to report an emergency to a controller, the NEXCOM system will provide priority access, and allow the pilot to break in immediately.

To resolve the spectrum depletion problem, NEXCOM splits a frequency into four channels, each of which can be used for voice or data. VDL-3 uses time division multiple access (TDMA) to divide a frequency assignment into time slots, and then uses precise timing to schedule the transmissions. As a result, a frequency that once could accommodate only one analog voice transmission now can carry up to four simultaneous transmissions.

Like Cell Phones

"Basically, VDL-3 is the same technology used in cellular phones," Salvano says. "But obviously the FAA requirements–which involve safety of life services–demand much higher reliability and integrity."

He adds that the question of losing both voice and data communications in case of an airborne system’s failure has been addressed. "The system we’ll deploy for ATC purposes will be triply redundant, with the same integrity for voice and data," says Salvano. "But that wouldn’t preclude usage of another means of available communications, such as analog voice or another digital transmission. And in the current plan, we would never–at least in the foreseeable future–transition the emergency channel, 121.5. That will stay analog," he states.

The system "is heavily backed up," agrees Tom Kabaservice, Harris’ NEXCOM chief engineer. "Just as in today’s system, where you have alternate sites in case one goes down, the same principle is built into the Mode 3 infrastructure. You could actually route data to other systems through the ATN network, if one system is temporarily unavailable."

The airborne software for VDL-3 initially will be certified to DO-178B, Level D, which is adequate for the non-critical messaging currently used for CPDLC. However, the transmission of critical ATC messaging, involving directions for aircraft movement, without audio backup, would require an upgrade to DO-178B, Level C. "We have already started upgrading our verification and validation testing to show compliance with Level C," says Collins’ Guzak.

FAA believes that NEXCOM is on schedule, meeting its target goals. "We’re pursuing this new VDL-3 technology, such that we will have the multimode [ground] radios in deployment, the avionics certified, and the ground system available during calendar year 2005," says Salvano. "So then we can look at the business case–take that [information] to the JRC and ask, do we want to make the decision and when do we want to make it?"

NEXCOM and VDL-2

While the NEXCOM program continues to meet its target milestones, the expanded use of VDL-2 for controller pilot data link communications (CPDLC) is stalled–at least in the United States. A Federal Aviation Administration (FAA) decision last May put on hold plans to expand CPDLC beyond the Miami air route traffic control center (ARTCC) sector to seven additional centers (July 2003). In fact, Europeans may take the lead in data link messaging by implementing a 12-station Eurocontrol Link 2000+ network, using a VDL-2 aeronautical telecommunications network (ATN) provided by ARINC. VDL-2 is being installed in Japan, too.

FAA firmly denies that CPDLC in the United States has been halted. Agency officials say it only has been deferred–primarily because of financially distressed airlines’ inability to equip their fleets with necessary airborne equipment. "So it wasn’t economically imperative for us to spend more money to expand the program," says Dan Salvano, FAA’s director CNS systems.

Halted or deferred, FAA’s decision shifts the agency’s priorities to advancing NEXCOM and VDL-3. The agency remains firm in its priorities for NEXCOM. VDL-2 was never intended for flight-critical air traffic control (ATC) messaging, FAA officials contend. Nor do they agree that VDL-2 ground stations should be upgraded to VDL-3.

"Because [VDL-2] was designed to be an AOC [airline operational communications] system, it has different criteria from an air traffic control system," Williams adds. "We aren’t precluding use of VDL-2, but VDL-2 and VDL-3 do different things."

Salvano explains that, while VDL-2 in the Miami ARTCC sector has been described as a "shared network" for AOC and ATC communications, it provides a "very limited message set that is not time-critical. As soon as you go to time-critical messaging, you have to look at other requirements."

Nevertheless, Salvano believes valuable data is being collected from the Miami operations and that expansion of CPDLC to additional centers "would be considered in the future, when justified by increased [airline] equipage, experience and benefits."

Some believe VDL-2 and VDL-3 can coexist. "They’re complementary in many ways," says Harris’ Tom Kabaservice, the company’s NEXCOM chief engineer. "Mode 2 is good for broad ground-to-air messages, [while] Mode 3 is optimized for short secure messages, like clearances."

Whether "an interim step" or not, ARINC has a sizable investment in the VDL-2 ground stations they have installed. The decision to defer expansion of CPDLC was a financial blow to the Annapolis, Md.-based company. ARINC installed and now operates 13 ground stations that serve the Miami ARTCC, including three on offshore islands. It has another 140 stations installed in other parts of the United States, with plans to have a total of 160 U.S. stations by the end of 2003, according to Ed Montgomery, ARINC vice president, aviation and air traffic services.

Meanwhile, some airlines, including American, Continental, FedEx and overseas carriers, are continuing to equip their aircraft for Mode 2 operations in the Miami center airspace and also for Eurocontrol’s operational CPDLC program, called Link 2000+. In 2000, Eurocontrol implemented 8.33-kHz spacing to stave off voice frequency congestion, and it plans to supplement it with Mode 2 data link messaging. For Link 2000+, the agency also plans a broader message set than the one used by FAA in Miami.

ARINC now looks to Europe to advance VDL-2. It has been awarded the contract as the Link 2000+ service provider and is implementing a 12-station VDL-2 communications network that will feed into the Maastricht upper area control center. Spanning five countries, the network was scheduled to be ready for operation in October 2003.

Link 2000+ "is a peer program to the FAA’s CPDLC program in that the Europeans are implementing CPDLC services over the VDL-2 ATN infrastructure," explains Sarah McClellan, director of engineering services with ARINC in London. While ARINC’s component is up and running, the Link 2000+ program requires that airborne avionics be complete and validated, she explains. Scandinavian Airlines System (SAS), equipped with Rockwell Collins avionics, will be the first carrier to use the Link 2000+ VDL-2 system operationally, she adds. Other airlines are expected to be using it by mid-2004.

Meanwhile, ARINC is moving forward with a similar system in Asia. Working with Avicom (owned primarily by Japan’s JAL and All Nippon Airlines), the communications provider has installed two VDL-2 ground stations, which are now operational in Japan. And the company plans to install another eight stations that are to be operational in early 2004.

ARINC also is talking to other ATC providers in Asia, according to Heament Kurian, the company’s director of airline programs, Asia-Pacific. In fact, ARINC has formed a partnership with two organizations: Aviation Data Corp. of China, the primary data link provider in People’s Republic of China, and Aero Thai, in Thailand.